A variety of devices exist which may be implanted in a patient's body to supplement or replace natural body functions. Typically, devices may be used to assist the heart in maintaining the steady pumping action needed to sustain life, to control bladder functions, to assist in countering pain-producing nerve impulses, and to control the infusion of various solutions into the body. Such devices may be implanted in the patient for long periods of time, during which the patient may encounter a variety of situations placing different demands on the patient's body. These demands may be transient and substantially random or they may be recurring, and display a circadian or other cycle. Preferably, an implantable body function assistant device should, therefore, be capable of adapting to changing physiologic needs.
In the developing generation of body function assistance devices, digital electronics are replacing analog electronics, which were originally used in such devices. Using digital techniques, body function assistance devices may be made which are more versatile than analog devices. Digital counters and storage registers, combined with improved techniques for communicating information between an external device and an implanted device, make it possible to vary the output parameters of a digital device to suit a variety of physiologic conditions. Even digital devices, however, have generally not analyzed changing physiologic needs and generated a response which is interactive with the analysis, without external intervention.
The electronics art has now developed microprocessors, devices which incorporate the electronic components necessary to perform arithmetic calculations and logic functions with the small size needed for implantable devices. A microprocessor has the capability of accepting data from various sensors, analyzing the data, and generating a response appropriate for the particular analysis without external intervention. Such devices, however, have a relatively high power consumption level. Moreover, if the operating routine of an implanted body function device is actually changed, random access memory (RAM) is typically required. Use of RAM requires considerably more energy than does read only memory (ROM), where the instructions are fixed in the memory. A microprocessor-based body function assistance device capable of responding to changing physiologic needs would, therefore, require an optimized program structure to minimize power consumption while responding to both transient and cyclic physiologic needs. Excessive power consumption could substantially reduce the useful life of an implanted device, which has, typically, a lithium battery power supply, which is a finite source of energy.
These, and other problems, have been solved by Applicants herein for an implantable body function assistance device.